1. Field of the Invention
The present invention generally relates to a small type fuse for use in a high-voltage circuit (hereinafter sometimes referred to simply as a "high-voltage fuse") and particularly to a "high-voltage fuse" wherein two pieces of a fusible element thereof, which remain therin immediately after the fusible element is severed by the passage of overcurrent through a high-voltage circuit, are separated from each other by a distance sufficient to prevent occurence of a surplus arc therebetween, thereby enhancing the high-voltage circuit's capability of withstanding high-voltage without disruptive discharge.
2. Description of the Prior Art
In a conventional fuse employed in a high-voltage circuit which is contained in a device such as a microwave cooker operating at a high voltage of several kilovolts, after a fusible element thereof is melted by heat generated when overcurrent flows therethrough and is finally broken into two pieces which thereafter operate as electrodes, breakdown of air insulation between the remaining pieces of a fusible element (hereinafter sometimes referred to as "electrodes") can occur and further cause an electric arc therebetween under conditions that the open-gap distance between the "electrodes" is narrow and that a voltage applied therebetween is high. Such phenomenon (that is, the breakdown of air insulation between the "electrodes") cannot be prevented when a fuse employed in a common low-voltage circuit operating at a voltage of below 250 volts is used in such a high voltage circuit. Disadvantageously, surplus flow of the arc current often causes considerable damage to components provided in the device.
Moreover, as is frequencly the case with the conventional "high-voltage fuse", when a common fusible element is melted and further severed by the heat generated from the over-current flowing therethrough, the value of a voltage developed across the fuse at the time of severing of the fusible element, that is, the value of a fusing voltage of the conventional "high-voltage fuse" is very low (for instance, about zero). In such a case, the interval between the "electrodes", that is, the distance between two cut ends of the remaining pieces of the fusible element facing each other is so small that a surplus arc may be induced thereafter.
In view of such a problem, there has been provided a conventional "high-voltage fuse" of a type such as shown in FIG. 4 wherein a spring 7 is connected in series with a fusible element 1 by soldering thereto so that the interval between the "electrodes" formed on the heels of the severing of the fusible element 1 is enlarged by contraction of the spring 7. Further, in this figure, reference numerals 4, 5 and 6 indicate a pair of end caps, a fuse tube and a layer of solder used to connect the fuse to the high-voltage circuit (not shown), respectively.
However, in a fuse of such a type in which a fusible element is connected in series with a spring, the fusible element is constantly tensioned by the spring and is thus placed under mechanical stress. Moreover, it is to be noted that ordinarily, differences in magnitude of tension among individual springs used in the fuses of such a type are not negligible. Thus, characteristics of melting and severing of the fusible element (hereafter referred to simply as "fusion") of the conventional "high-voltage fuse" of such a type are not stable.
Furthermore, if an electrical accident occurs and results in a large current flow in the "high-voltage fuse" of such a type, the spring, as well as the solder which is used to connect the fusible element with the spring, can be instantly converted into metal vapor and further an arc can occur in the fuse. The amount of the metal, which serves as a source of the arc, contained in the vapor is so great that the arc can continue for a period of time which is long enough to cause destruction of a fuse tube exposed to the arc.
In addition, the conventional "high-voltage fuse" of such a type has drawbacks that material of an available fusible element and the diameter thereof are restricted to those which enable tensile strength of the fusible element to match with the tension of the spring and that thus, a fuse of small current breaking capacity cannot be produced.
Accordingly, it is an object of the present invention to eliminate the above described defects of the conventional "high-voltage fuse" of such a type and to provide an improved "high-voltage fuse" which can prevent occurence of a surplus arc after "fusion" therein.